P1928R15 std::simd --- merge data-parallel types from the Parallelism TS 2

* Add closing parenthesis in [simd.reductions] p3.
* Add namespace std to simd_flags, basic_simd, and basic_simd_mask
* Add comma after 'e.g.'
* Add \rSec3[simd.expos.defn]{Exposition-only helpers} (missing sibling)
* Remove \iref from simd.expos.abi] (5.3), already in (5.2)

Fixes #7430
Fixes cplusplus/papers#670

Author: mattkretz

source/compatibility.tex

@@ -186,7 +186,8 @@
 \libheaderrefx{hazard_pointer}{hazard.pointer.syn},
 \libheaderrefx{inplace_vector}{inplace.vector.syn},
 \libheaderref{linalg},
-\libheaderref{rcu}, and
+\libheaderref{rcu},
+\libheaderref{simd}, and
 \libheaderrefx{text_encoding}{text.encoding.syn}.
 Valid \CppXXIII{} code that \tcode{\#include}{s} headers with these names may be
 invalid in this revision of \Cpp{}.

source/lib-intro.tex

@@ -1224,6 +1224,7 @@
 \tcode{<semaphore>} \\
 \tcode{<set>} \\
 \tcode{<shared_mutex>} \\
+\tcode{<simd>} \\
 \tcode{<source_location>} \\
 \tcode{<span>} \\
 \tcode{<spanstream>} \\